The Importance Of Planetesimal-driven Migration And Collisional Grinding In Terrestrial Planet Formation

Author Block

David A. Minton1, H. F. Levison11Southwest Research Institute.

Abstract

Planetesimal-driven migration has come to be understood as an important process in the evolution of the orbits of the giant planets. We investigate here whether planetesimal-driven migration may have been important while rocky planetary embryos were accreting within in a massive swarm of planetesimals in the inner solar system, where "embryo" is defined to as lunar to Mars-mass bodies. Planetesimal-driven migration becomes important if embryos can migrate through a planetesimal disk at a faster rate than the rate of embryo growth; migrating embryos can reach embryo-free zones of the disk before new embryos have a chance to grow there. Migration rates of Mars sized embryos are comparable to embryo formation rates in a planetesimal disk containing ~2 times or greater the surface mass density of the standard Minimum Mass Solar Nebula model. A more massive disk is not a problem, because we show that collisional grinding and mass loss due to embryo growth is an important but heretofore neglected process. Planetesimal-driven migration allows growing embryos to be far more mobile during the runaway stage than has been assumed, leading to very different outcomes for planet formation than have been modeled to date. One possible outcome of a migrating embryo model of terrestrial planet formation is that the outward migration of Mars may have been responsible for keeping its mass small. A consequence of this outward migration is that Mars may have populated the inner asteroid belt with planetesimals, directly analogous to the resonant Kuiper belt objects that were presumably populated by Neptune's outward migration. These resonant objects may have been an important contributor to terrestrial planet impacts when they became unstable due to the later migration of the outer giant planets.

Embargoed: All findings are embargoed until the time of presentation at the meeting. "Time of presentation" means the start time of the Oral or Poster paper session in which the paper will be given, or the time of the corresponding press conference (if any), whichever comes first.